In recent years, piezoelectric vibrators using crystals or the like have been used in mobile phones or personal digital assistants, as a time source, a timing source such as a control signal, a reference signal source and the like. Various types of piezoelectric vibrators are provided, an SMD type piezoelectric vibrator is known as one. With this type of piezoelectric vibrator, generally, a three layer structure type, in which piezoelectric substrates formed with a piezoelectric vibrating reed are bonded so as to be interposed from above and below by a base substrate and a lid substrate, is known. In this case, the piezoelectric vibrating reed is accommodated in a cavity (a sealing chamber) formed between the base substrate and the lid substrate.
Furthermore, in recent years, a two layer structure type has also been developed instead of the three layer structure type. This type of piezoelectric vibrator has the two layer structure, in which the base substrate and the lid substrate are directly bonded to each other and the piezoelectric vibrating reed is accommodated within the cavity formed between both substrates. The piezoelectric vibrator of a two layer structure is superior in that thinning can be promoted as compared to the three layer structure and is preferentially used.
However, in a method of manufacturing the piezoelectric vibrator, there is need to perform a process of raising a degree of vacuum in the cavity and making a series resonance resistance value (R1) follow up within a predetermined range. Since the degree of vacuum in the cavity is a factor that affects the frequency (the resonance frequency) of the piezoelectric vibrating reed, this process is one of the crucial processes.
Usually, the process is performed before a minute regulation process (a process of minutely regulating the frequency so that the piezoelectric vibrating reed ultimately vibrates within the range of the nominal frequency), and at the timing when the minute regulation process is performed, there is a need to put the series resonance resistance value (R1) within a suitable predetermined range in advance.
Herein, a method is known of regulating the series resonance resistance value (R1), a method of using a getter material, which is a metallic film such as aluminum, provided in the cavity (for example, see Patent Document 1).
This method, firstly, heats, evaporates and activates the getter material using a laser or the like. Then, the activated getter material absorbs gas mainly consisting of oxygen in the cavity by a chemical reaction while being evaporated. As a consequence, the degree of vacuum in the cavity can be raised and the series resonance resistance value (R1) can be regulated. In addition, a method of regulating the series resonance resistance value (R1) using the getter material is called gettering.
[Patent Citation 1] JP-A-2003-142976
However, in the gettering of the related art, the following problem remains.
Firstly, in a case where the getter material is arranged on the piezoelectric vibrating reed, the piezoelectric vibrating reed is also heated when heating the getter material using a laser. For that reason, there is a chance that the piezoelectric vibrating reed may be affected by the heating.
On the other hand, in a case where the getter material is formed on the substrate around the piezoelectric vibrating reed, there is a high chance that a part of the getter material, which is evaporated and scattered when the getter material is heated using a laser or the like, becomes attached to the piezoelectric vibrating reed. Particularly, the nearer the irradiation position of laser, the easier the evaporated getter material would attach. Incidentally, when the getter material is attached to the piezoelectric vibrating reed, there is a concern that the frequency of the piezoelectric vibrating reed may change. The change in frequency differs depending on the attachment position of the getter material. Particularly, when the getter material is attached to a front end side of the vibration arm portion, the frequency tends to be lowered, and when the getter material is attached to a proximal end side of the vibration arm portion, the frequency tends to be raised. Furthermore, it is known that the greater the attachment amount is, the greater the change amount is.
In this manner, there is a high chance that the frequency of the piezoelectric vibrating reed before and after the gettering is changed by the attachment of the getter material. Usually, the piezoelectric vibrating reed is subjected to a rough regulation process before the gettering, and the frequency regulation is performed so as to be limited within a range that is slightly wider than a nominal frequency of the object. Moreover, after regulating the series resonance resistance value (R1) by the gettering, the minute regulation process is performed to ultimately put the frequency into the range of the nominal frequency. For that reason, when the frequency is changed before or after the gettering, the frequency adjusted to some degree by the rough regulation process is changed. Thus, there is a risk not only that the minute regulation process may be considerably difficult, but also that the stable vibration property may not be obtained.
The invention was made in view of the above circumstances, and an object thereof is to provide a piezoelectric vibrator that does not force a load due to the heating with respect to the piezoelectric vibrating reed and can perform the gettering without generating the frequency change.
Furthermore, another object thereof is to provide an oscillator having the piezoelectric vibrator, electronic equipment and a radio-controlled timepiece, and a method of manufacturing a piezoelectric vibrator.